Mitigating Motion Sickness by Anticipatory Cues

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper is a systematic experimental study that attempts to clarify the effectiveness of presenting future motion information using audio and haptic cues in reducing motion sickness.

The fact that presenting future information is effective in reducing motion sickness has been said qualitatively, and several papers have been published demonstrating this, but the effects reported in the literature have been variable. Furthermore, there has been little research that has clearly investigated differences due to sensory modality. In contrast, this study contributed to the literature by conducting a systematic comparison by limiting the experiment to specific motion stimuli in the forward and backward movement used in a laboratory experiment, making it possible to compare with previous studies.

The research motivation, objectives, methods, results, etc. are fully described, and its contribution is clear for me. 

The only comment is as follows.

At the end of 4.4 Summary, there is a statement that

"Participants are prone to making larger prediction errors for more unpredictable motion stimuli, which could explain why anticipatory cues generate a larger effect. This suggests that anticipatory cues may be even more advantageous during real life car driving when assuming there will be greater variability in driving maneuvers." 

While this statement is understandable about the increasing difficulty of motion prediction, the increased complexity of vehicle motion makes it difficult to even present motion prediction cues using auditory, haptics, etc., and it is difficult to say that this will necessarily result in greater effectiveness. This point should be further discussed.

Author Response

This paper is a systematic experimental study that attempts to clarify the effectiveness of presenting future motion information using audio and haptic cues in reducing motion sickness.

The fact that presenting future information is effective in reducing motion sickness has been said qualitatively, and several papers have been published demonstrating this, but the effects reported in the literature have been variable. Furthermore, there has been little research that has clearly investigated differences due to sensory modality.

In contrast, this study contributed to the literature by conducting a systematic comparison by limiting the experiment to specific motion stimuli in the forward and backward movement used in a laboratory experiment, making it possible to compare with previous studies.

The research motivation, objectives, methods, results, etc. are fully described, and its contribution is clear for me. 

The only comment is as follows.

At the end of 4.4 Summary, there is a statement that

"Participants are prone to making larger prediction errors for more unpredictable motion stimuli, which could explain why anticipatory cues generate a larger effect. This suggests that anticipatory cues may be even more advantageous during real life car driving when assuming there will be greater variability in driving maneuvers." 

While this statement is understandable about the increasing difficulty of motion prediction, the increased complexity of vehicle motion makes it difficult to even present motion prediction cues using auditory, haptics, etc., and it is difficult to say that this will necessarily result in greater effectiveness. This point should be further discussed.

We agree with the reviewer that further research is needed to determine the design and implementation of cues for motions with multiple degrees of freedom. We have added the following text to lines 439-445:

“Determining which and how those maneuvers should be announced requires further investigation. For example, motions that are not provocative should not be announced as providing unnecessary cues may result in passengers disengaging the cueing system [28]. Unforeseen maneuvers which the automated vehicle did not anticipate may not allow sufficient time for providing a directional anticipatory cue. However, such events should be incidental as automated vehicles are generally able to predict their motion well.”

Reviewer 2 Report

Comments and Suggestions for Authors

The authors presented an investigation into the mitigation of motion sickness in car passengers through anticipatory auditory and vibrotactile cues. The study’s rationale is well-founded, highlighting the disparity in motion sickness experiences and the potential benefits of anticipatory cues in automated vehicles.

I appreciate the authors' focus on comparing auditory and vibrotactile cues in the context of automated vehicles. Given the increasing interest in autonomous driving technologies, this is both timely and relevant.

A room for Improvement is always available. The manuscript mentions mixed evidence from prior studies but the nature of these findings may be addressed in other perspectives. Providing a brief overview of this mixed evidence could help contextualize the current study’s contributions.

The age group of the people involved in the study and their ergonomic posture may also be addressed. 

While the paper concludes that anticipatory cues have a small overall effect, it would be beneficial to specify what measures or outcomes were missed to determine this effectiveness. This would provide clearer insights into the practical implications of the future findings.

There may be a suggestion to investigate how the effectiveness of anticipatory cues can be enhanced is valuable even high-performance computing could be utilized.  However, offering specific potential avenues for future research could strengthen and provide more concrete guidance for subsequent studies in a real vehicle rather than laboratory-level studies.

Overall, the manuscript is well organized and effectively sets the stage for the study and its significance. Addressing the points mentioned above could further enhance its clarity and impact.

Author Response

The authors presented an investigation into the mitigation of motion sickness in car passengers through anticipatory auditory and vibrotactile cues. The study’s rationale is well-founded, highlighting the disparity in motion sickness experiences and the potential benefits of anticipatory cues in automated vehicles.

I appreciate the authors' focus on comparing auditory and vibrotactile cues in the context of automated vehicles. Given the increasing interest in autonomous driving technologies, this is both timely and relevant.

A room for Improvement is always available. The manuscript mentions mixed evidence from prior studies but the nature of these findings may be addressed in other perspectives. Providing a brief overview of this mixed evidence could help contextualize the current study’s contributions.

We agree with the reviewer that a discussion of the mixed evidence on the effectiveness of vibrotactile cues provides context for the contribution of the current study. We dedicate a paragraph on this discussion on lines 58-77:

“Whereas the vibrotactile cues did not mitigate motion sickness significantly in the study of Reuten et al. [21], auditory cues were effective in a study using the same motion apparatus, an equally provocative motion stimulus, and a similar experimental protocol [9]. Moreover, we found a significant reduction in motion sickness from anticipatory vibrotactile cues in a test track study [22]. How can we explain this discrepancy? A first explanation concerns a difference in the unpredictability of the used motion stimulus. … An alternative explanation is that auditory cues are more effective than vibrotactile cues, which makes it easier to demonstrate their effect. … To conclude, a direct comparison between anticipatory auditory and vibrotactile cues using the same motion stimulus is needed to elucidate their effect.” 

The age group of the people involved in the study and their ergonomic posture may also be addressed. 

In addition to providing the average age of our sample, we have included the min-max range on lines 99-102:

“All of our participants (13 males) indicated to be in good overall health, free from self-known vestibular disturbances, and have experienced symptoms of car sickness in the last five years. Participants’ ages ranged from 21 to 60 years old, with a mean of 33 years.”

We added more details on the participant’s ergonomic posture on lines 113-114:

“The sled offered an enclosed cabin in which participants were seated on a rally seat with a head- and footrest (Figure 1b).”

While the paper concludes that anticipatory cues have a small overall effect, it would be beneficial to specify what measures or outcomes were missed to determine this effectiveness. This would provide clearer insights into the practical implications of the future findings.

Our main measure of interest was the Motion Illness Symptoms Classification (MISC) scale. We based our analysis approach on the assumption that anticipatory cues result in a reduction in motion sickness by a certain fraction (e.g. 25%), rather than by a fixed value (e.g. 4). The latter would yield nonsense results for low MISC values, as a reduction of 4 would imply negative MISC values when starting at MISC values below 4. We have elaborated this on lines 203-209:

“In our first laboratory study [21], we developed a way to express the effectiveness of the anticipatory cues during the whole session in one value. Here we will use the same data analysis approach. In our approach, we assumed that the cues would mitigate motion sickness by a certain fraction (e.g., 25%) rather than by a fixed value (e.g., 4 MISC classes). The latter would yield nonsense results for low MISC scores, as a reduction of 4 would imply negative MISC values when starting at MISC values below 4. We use the measure R, denoting the relative reduction in motion sickness symptoms in the anticipatory session relative to the control session.”

As the MISC can be taken as a measure of motion sickness development [27], a positive value of  can be interpreted as less motion sickness progression. We provide readers guidance to the interpretation of  by transforming this measureinto a percentage reduction of symptoms (), elaborated on lines 234-238:

“To provide the reader some intuition for our measure, we provide a conversion of  to a percentual change in MISC scores (i.e., ) in Supplementary Figure S2. Note that for , exchanging  and  only results in a change of sign, whereas has an asymmetrical distribution.”

The results from the experiment did not demonstrate a significant reduction in motion sickness, but there were several reasons which suggested that the anticipatory cues did mitigate motion sickness (lines 329-341). The results from an internal meta-analysis confirmed this (section 4.2). This suggests that experiments on the effectiveness of anticipatory cues need high statistical power. We explicate this on lines 378-380:

“For these two reasons, we interpret the observed overall effect of anticipatory cueing the result of more statistical power. Studies investigating the effectiveness of anticipatory cues thus require high statistical power.”

 The reduction in motion sickness progression we found in our current study corresponds to a 11% reduction in motion sickness, lower than the 40% reduction we observed in a test track study. We speculate that increasing the number of degrees of freedom may increase the effectiveness of anticipatory cues. These aspects are elaborated on lines 430-435:

“When converting this reduction to a measure of percentage change, the anticipatory cues reduced motion sickness by 11%. This percentage is much smaller compared to a reduction from vibrotactile cues of 40% we observed in a test track study in which we used the same data analysis approach [22]. Taken as a whole, the pattern of findings across our studies suggest that anticipatory cues are of greatest benefit to participants when motions consist of more degrees of freedom.”

There may be a suggestion to investigate how the effectiveness of anticipatory cues can be enhanced is valuable even high-performance computing could be utilized.  However, offering specific potential avenues for future research could strengthen and provide more concrete guidance for subsequent studies in a real vehicle rather than laboratory-level studies.

In line with the comment from Reviewer 1, we have included some suggestions for further research on lines 439-445:

“Determining which and how those maneuvers should be announced requires further investigation. For example, motions that are not provocative should not be announced as providing unnecessary cues may result in passengers disengaging the cueing system [28]. Unforeseen maneuvers which the automated vehicle did not anticipate may not allow sufficient time for providing a directional anticipatory cue. However, such events should be incidental as automated vehicles are generally able to predict their motion well.”

Overall, the manuscript is well organized and effectively sets the stage for the study and its significance. Addressing the points mentioned above could further enhance its clarity and impact.